The eye is certainly capable of moving to any point on the
page extremely rapidly. Yet, when we browse, we do not move
about randomly around the printed page. Typically, we move to
the next paragraph, next line, or previous word. This seems to
indicate that the eye infers some structure in the printed
document, which is used to move around effectively. Since each
of these actions are being performed extremely rapidly, owing
to the eye's inherent scanning ability, these atomic actions
are difficult to pinpoint.

We therefore conjecture the following: Every
well-formatted document presents inherent logical structure,
which the eye is capable of perceiving. All visual browsing
actions can be characterized as movements around this
structure.